The present invention relates to an injection device for administering drugs in a safe and reliable way.
The handling and safety aspects of injection devices, having a certain degree of automatic functions, as well as immediate accessibility in emergency situations are issues that attract a lot of attention when developing this type of device.
A few of these devices have safety aspects like a two-step operation before the injection is activated in order to avoid unintended activation, for example if the user comes in contact with the trigger button before the device is placed at an injection site. However many of these solutions are rather bulky and rely also on many components acting or co-operation and in sequence, one trigging another, which may lead to a mal-function, or that the device becomes complicated, hence not user friendly.
One device utilising a high degree of automation is described in International Application Publication WO 02/74774. The device is an auto-injector whereby the injection can be activated by a push button, i.e. penetration and injection, but only when the front end of the injector is pressed against the injection site. It is designed as a kind of two-step operation where the order has to be: pressing the injector at the site and then depressing the button. Any other order of sequence will not result in an activation of the device. This ensures that the injector cannot be accidentally activated by merely pushing the button nor even pushing the button and then pressing the front end.
U.S. Pat. No. 5,137,516 discloses another type of automatically operated injection device. The user first presses the device against the skin in order to move an internal shaft and a sleeve assembly. An actuating button is then depressed, causing a button arm to spread the arms of a retention clip. The separation of these arms releases the head of the plunger rod, which is then moved forwardly under the force of a main coil spring. The plunger rod first moves the entire syringe against the force of a syringe spring. Once the needle has penetrated the skin, the syringe plunger is depressed by the plunger rod, causing the syringe to empty. The main spring of the patented device may be recocked upon reloading of a new syringe assembly. Such reloading is accomplished by a force applied by the syringe piston directly upon the pusher rod of the device.
Even though the above mentioned devices have proved to function well and display a high degree of safety and user-friendliness there is always a desire for improvements of such devices, among them being the design of the mechanism in order to simplify the manufacture and assembly in order to reduce costs but at the same time maintain or even improve the reliability of the function of the device.